Field of the Invention
The present invention relates to a Wireless Local Area Network (WLAN) system, and more particularly, to a method of a station (STA) transmitting a data frame in a WLAN system.
Discussion of the Related Art
Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
In order to overcome a limit to the communication speed that has been considered as weakness in the WLAN technique, an IEEE 802.11n standard has recently been standardized as a technology standard. The object of the IEEE 802.11n standard is to increase the speed and reliability of a network and to expand the coverage of a wireless network. More particularly, in order to support a High Throughput (HT) having a data processing speed of 540 Mbps or higher, minimize a transmission error, and optimize the data rate, the IEEE 802.11n standard is based on Multiple Inputs and Multiple Outputs (MIMO) technology in which multiple antennas are used on both sides of each of a transmitter and a receiver.
As the propagation of the WLAN is being activated and applications employing the WLAN are being diversified, in an STA, a necessary for a new WLAN system for supporting a higher throughput than the data processing speed supported by the IEEE 802.11n standard is on the rise. The next-generation WLAN system supporting a Very High Throughput (VHT) is the next version of the IEEE 802.11n WLAN system and is one of IEEE 802.11 WLAN systems which have recently been proposed in order to support a data processing speed of 1 Gbps or higher in an MAC Service Access Point (SAP).
The next-generation WLAN system supports the transmission of a Multi-User Multiple Input Multiple Output (MU-MIMO) scheme in which a plurality of non-AP STAs accesses a radio channel at the same time in order to efficiently use the radio channel. According to the MU-MIMO transmission scheme, an AP can transmit a frame to one or more MIMO-paired non-AP STAs at the same time.
The AP and the plurality of MIMO-paired non-AP STAs may have different capabilities. A bandwidth, a Modulation Coding Scheme (MCS), and Forward Error Correction (FEC), that may be supported, may differ according to a kind of the non-AP STA, purposes, a channel environment, etc. If a channel bandwidth to be used to transmit STAs having different capabilities can be freely controlled within a TXOP (transmission opportunity) period, there may be generated interference with an AP or an STA or both which transmit and receive frames in a frequency band. Accordingly, reliability may become problematic when the frames are transmitted and received. Accordingly, there is a need for a method capable of transmitting a data frame to STAs with different capabilities while not generating interference with another AP or another STA or both within the TXOP period.